PORTLAND, Ore.  An exclusive new KATU poll shows Sen. Barack Obama building his lead over Sen. Hillary Clinton in Oregon's 2008 primary.

The poll, conducted by SurveyUSA exclusively for KATU News, showed Obama leading Clinton by 9 points among the 77 percent of likely voters who have already returned a ballot.

When taking into consideration all likely voters, including those who say they plan to return their ballot before the 8 p.m. deadline on Tuesday, Obama defeats Clinton 55 percent to 42 percent. That's a two-point increase for Obama since last week's poll.

The margin of error is 4 percent.

Click here for full details on the poll.

Though the presidential candidates have all come and left the state over the last week, plenty of others, from local city council hopefuls to U.S. Senate contenders, are still out there campaigning, as election officials brace for tens of thousands of mail ballots to pour in before the voting deadline.

Oregon's unique vote-by-mail election system meant many people could get their ballots in before the 20th, but election workers were emptying ballot drop-off boxes early Tuesday morning and said they planned on a long day of scooping up boxes of votes.

Many candidates and voters in Oregon were weary from months of campaign stops, relentless TV ads, and visits from candidates.

"I was exhausted a few days ago, but then I got a full night's sleep," said Oregon House Speaker Jeff Merkley, who is in a too-close-to-call race with Portland lawyer Steve Novick for the Democratic Senate nomination. "As you get closer to the end of the campaign, there are fewer decisions to make. You just keep shaking hands and making phone calls."

Merkley spent the day hopscotching from Portland to Corvallis to Eugene and back up to Salem, traveling much of the day with Gov. Ted Kulongoski. Novick got up at 4:30 a.m. Monday and traveled to Eugene, where he spent the morning rush hour waving to commuters coming off the Ferry Street Bridge.

"People were honking back at me," Novick said. "Things feel good out there. We're getting a really good response."

Whoever wins the Democratic primary, there won't be much rest for the weary. With just five months to go until the general election against incumbent Sen. Gordon Smith, outreach to disaffected Republicans and Oregon's large pool of nonaffiliated voters will have to start immediately, Merkley noted.

The Novick-Merkley race looks like the nailbiter of the night, despite a poll released Monday by Suffolk University of Boston suggesting that Clinton trailed Obama in the state by only four percentage points, 45 percent to 41 percent.

But David Paleologos, the director of the Suffolk Political Research Center, said the poll found both a high rate of undecided voters and those who declined to answer, which may have skewed the results slightly.

"We don't think (Oregon) is a 20-point win for Obama, but it's likely high single digits, eight or nine percent, and it could be above that," he said. "I am confident about the outcome; it's just a question of the margin and who brings out their vote."

In-state pollsters have pegged Obama's lead at more like eight to 12 percentage points, a margin suggested by the 75,000 people who turned out to hear him speak in Portland on Sunday.

If it were a close race, Portland pollster Tim Hibbitts added, Clinton and Obama "would be here in Oregon campaigning through Tuesday, and neither of them is doing that."

Lisa Grove, a Portland-based Democratic pollster who is not working for either candidate, noted that the Suffolk poll may not have taken into account all the newly registered Democrats, about 115,000 since the beginning of the year, many of whom are between the ages of 18 and 30. Nationally, Obama has had a distinct advantage with younger voters.

The Clinton campaign is ceding little ground, extending former first daughter Chelsea Clinton's visit to the state to Monday. Still, Josh Kardon, chairman of Clinton's Oregon campaign, said it appears Obama is ahead.

"Hillary has faced a very steep uphill climb in Oregon, but in the last week we have seen her make progress with previously undecided voters," Kardon said.

Voters just sounded happy to have their chance to weigh in on such a historic election, since few people had expected the presidential race to still be competitive by the time it got to Oregon.

"She was a great candidate, but there was no doubt who I was going to vote for," said LaRisha Baker, who works for Multnomah County and dropped off her ballot Monday, having voted for Obama. "It's just having those conversations about things people haven't been used to talking about in the open, and actually addressing health, and equity and disparities."

David Livermore, an environmental consultant from Portland said he was persuaded by Clinton's argument that she was the more experienced candidate.

"I liked the specifics of her details of her health care policy, the environmental issues that are going to face us in the next 10 to 20 years," he said.

Oregonians continue to return their ballots in large numbers - especially Democratic voters, Oregon Secretary of State Bill Bradbury said.

As of Monday afternoon, more than 440,000 Oregon Democrats had returned their ballots, or about 51 percent of the total number of registered Democrats. About 246,000 Republicans - or 37 percent of registered GOP voters - had turned theirs in by the same time.

Combined with an 19 percent turnout by nonaffiliated voters, total turnout for all voters is about 38 percent so far - well ahead of the 33 percent turnout at this point of the May 2004 presidential primary.

"It's thrilling to be involved in something that has so many people excited," Bradbury said.

Associated Press writer William McCall in Portland contributed to this report. 

(Copyright 2008 by The Associated Press. All Rights Reserved.)